Along with the advances of digital technology and improvement of data compression technology in recent years, optical disks such as DVDs (Digital Versatile Disk) are receiving greater attention as information recording media for recording information including, for example, music, movies, and photographs (hereinafter referred to as “contents”). Furthermore, more optical disk apparatuses are being used as information recording apparatuses for recording contents to disks as the price of the optical disk is becoming lower. It is to be noted that apparatuses for accessing information recording media are collectively referred to as “drive apparatuses”.
As for recordable optical disks (also referred to as “recording type disk”) that are commercially sold, there is a write-once type disk (write-once-read-many optical disk) to which information can be written only once (e.g., DVD+R, DVD-R) and a rewritable type disk (e.g., DVD+RW, DVD-RW).
Furthermore, the recording capacity of recording type disks is expected to further increase along with an increase in the amount of information contained in the contents. Furthermore, as a measure for increasing the amount of information recordable on a recording type disk, vigorous research and development being made on a recording type disk having multiple recording layers (hereinafter referred to as “multilayer recording type disk”) and an apparatus for handling the multilayer recording type disk (See, for example, Japanese Laid-Open Patent Application No. 8-96406).
It is to be noted that a single-sided dual layer DVD-ROM (DVD-ROM having two layers on one side of the disk) is being commercially sold as a read only memory disk having two recording layers. In the single-sided dual layer DVD-ROM, information on each recording layer is reproduced by irradiating a laser beam from one side and matching the focal point of the laser beam to each recording layer. That is, with the single-sided dual layer DVD-ROM, information can be reproduced without having to turn over (flip over) the disk. In the single-sided dual layer DVD-ROM, data is required to be recorded on both first and second recording layers (for example, Layer 0, Layer 1) of the disk. For example, supposing that Layer 0 is a recorded layer having data recorded thereto and Layer 1 is an unrecorded layer having no data recorded thereto, address information may be obtained and an address error may occur in a case where vibration or the like during a seek operation or a reproduction operation causes the laser beam to focus on Layer 1. Therefore, without having data recorded to both layers, the Dual Layer DVD-ROM will be determined to be a defective disk and may be unable to continue reproduction of data.
Meanwhile, since conventional drive apparatuses corresponding to a read only memory type optical disk are widely used, it is important that the contents recorded to the multilayer recording type disk can also be reproduced with a conventional drive apparatus. That is, the contents recorded to a recording type disk are required to be logically compatible with the conventional read only memory optical disk.
Therefore, in a case where a multilayer recording type disk is expected to be reproduced with a conventional drive apparatus, some kind of data is to be recorded in the unrecorded area (area where no contents are recorded) of the disk so that all of the multiple recording layers of disks have data recorded thereto. However, in a case where the amount of information contained in the contents is little with respect to the recording capacity of the multilayer recording type disk, a vast amount of time is required for recording dummy data in the unrecorded area of the disk. This may lead to degrading of recording performance. The degrading of recording performance may occur particularly with a rewritable multilayer recording type disk that conducts a formatting process in the background. Since contents can be recorded before a formatting process is actually completed, the rewritable multilayer recording type disk will have an undesired coexistence of a recorded area (area to which the contents are recorded), a dummy data area (area to which dummy data is recorded), and an unrecorded area (area to which no data is recorded) after the contents are recorded to the disk. Furthermore, in a process of providing logical compatibility with a read only memory optical disk, there is a risk that dummy data recorded to the disk in the formatting process may be overwritten. This results in further degrading of recording performance.